1. Field of the Invention
The present invention relates to an information retrieval system, method, and program for searching an answer to a spoken question.
2. Description of the Related Art
Conventionally, there has been proposed a number of question answering systems for a spoken question from a user and displaying a result of such a search or outputting the result by speech synthesis. In such a system, in general, an answer is generated by using a problem solution knowledge (database) which has been prepared in advance. In such a question answering system, in the case where an inputted question is ambiguous, it is difficult to generate an answer which the user wants to obtain.
There has been proposed a contrivance of making an additional question to the user if such an ambiguous question occurs and obtaining an answer to such an additional question from the user, thereby eliminating ambiguousness. For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-63209, there is described an information processing apparatus for: maintaining a candidate list having contents registered therein; calculating similarity of the contents registered in that candidate list based on a search condition inputted from another device; in the case where the calculated similarity is smaller than a predetermined threshold value, deleting the corresponding contents from the candidate list; in the case where a total number of contents remaining in the candidate list is equal to or greater than a predetermined number, presenting a question item to such another device; and further calculating the similarity of contents based on an additional search condition inputted from such another device.
In addition, in the conventional system, there has been conducted a research and development of a question answering type search for analyzing text information which is a question of a natural language sentence and searching a required answer from a document database based on a result of the analysis. This question answering type search is different from a general document search in that answers of questions are presented without any excess or shortage instead of being presented in units of documents. For example, an answer “3,776 m” to a question that “how high is Mt. Fuji?” is obtained.
Conventionally, in order to achieve a question answering for a spoken question, first, the spoken question must be converted to text information by means of speech recognition processing. However, in a question answering system for making a search from a document database, it is very difficult to cope with a case in which a speech recognition error occurs.
In the case where a search is made for a document by a spoken question of a natural language sentence, even if a speech recognition error is included in such a question, a search can be made for a document from a correctly recognized portion. However, in the question answering type search for making a search from the document database, if a recognition error occurs with a portion of an interrogative expression (such as how many meters or how many kilograms) for estimating an answer (type of answer such as length or weight), a search cannot be made for a proper answer.